Station selection system



Mardi 13, 1945. L, POTTS 2,371,311

STATION SELECTION SYSTEM Filed Feb. 1-. mil 2 Sheets-Sheet 1 JINVENTOR.

e4 LOUIS 11.1 0115 42 v BY TrbRNEY.

March 13, 1945. M. Po'rTs 2,371,311

- STATION SELECTION SYSTEM Filed Feb. 1, 1941 2 Sheets-Sheet 2 K FIG. 4

' INVENTOR. LOUIS u. POTTS ATTORNEY.

Patented Mar. 13, 1945 STATION SELECTION SYSTEM t Louis M. Potts,Evanston, Ill., assignor to Teletype Corporation, Chicago, 111., acorporation of Delaware 7 Claims.

The present invention relates to station selection systems and moreparticularly toprinting telegraph switching systems for interconnectingstations for telegraphic communication.

The principal object of the present inventionresides in the provision ofstation selecting mechanism for use in conjunction with start-stoptelegraph systems which will produce impulses that can be repeated bytelegraph repeating apparatus satisfactorily and which will effectivelyserve to operate conventional types of equipment for se lecting any oneof a plurality of stations.

The use of station selection methods by means of manual dial equipmentis equally desirable in printing telegraphy as it is telephony. From aconvenience and utility viewpoint it is proposed in accordance with thepresent improvement to so regulate standard dial apparatus by means oftelegraphic regulating and'periodicity safeguarding equipment as to makeits use in conjunction with start-stop telegraphic systems equallypractical. Toward this end a mechanical tie-up is effected betweenthedial apparatus and a startstop regulated shaft of a keyboardtransmitter whereby a station selecting dial of standard construction asknown in telephony is utilized for generating a. number of permutationcode signals which are composed of but a single line changecharacteristic during the entirety of the code combination so as toreproduce a number of similar signal impulses which may thereafter beused to operate station selecting switches after the manner of standardtelephone practice.

In carrying out this plan of operation, the permutation code signal forthe letter M has been chosen because it is composed of three successivespacing impulses followed by four successive marking impulses simulatingthereby an average length of dialing impulse for operating a stationselection switch. Since start-stop apparatus is, in fact, employed forthe purpose of generating these dial type signals with the dialequipment serving only as a means of initiating the start-stop equipmentand determining the number of signals, there is in effect produced astep-by-step pattern of signal which'is also in fact a start-stop signaland may therefore be received by start-stop apparatus such. as tapetransmitters, regenerative repeaters, etc., without impairment or needfor auxiliary apparatus to insure against improper responses.

In attaining the above andother objects of the present invention, theprincipal embodiment described hereinafter utilizes a rotary dial mech--anism operatively associated with a standard embodiment ofstart stoppermutation code transmitting keyboard. The dial may be operatedmanually by means of rotating a disc which is advanced by a fingermovement until a predetermined mark or fingerhole thereof attains astop.

Application February 1, 1941, Serial No. 376,962

The disc is thereafter released and automatically responsivemechanismrestores the disc to its normal position one step at a time. IAs each step is completed, and since a particular key lever of thetransmitting keyboard is held depressed during such operation, there isobtained the transmission of a number of character M signalscorresponding to the selecting index numeral which was dialed. Thus, ifa destination selecting index is comprised of, say, six impulses theparticular key leverand the transmitting apparatus are accordinglyoperated causing to be generated six permutation code signals of aparticular letter, which accordingly constitute that number ofstationselecting impulses in succession. These impulses are received at acentral station whereat they are elfective to operate selecting switchesto select an ultimate destination line over which start-stop messagesmay then be transmitted to a destination station.

The keyboard mechanism at each subscriber station is of standardarrangement and one of its character keys is depressed for a period oftime commensurate with the degree of rotation of the calling dial at thesame time the transmitter clutch is engaged for a corresponding numberof cycles and as each character code is transmitted the dial is steppedback toward zero position. When the station calling dial reaches itszero position the transmitter is, declutched, the key which had beenheld down is permitted to resume its normal condition, and thetransmission of code signals is arrested. Accordingly, it will beunderstood that the number of call signals generated through theintermediation of the keyboard mechanism will correspond with theangular position to which the calling dial is rotated and from which thecalling dial is returned to its zero position.

For a more comprehensive understanding of the present inventionreference may be had to the accompanying drawings and to the detailedspecification following hereinafter wherein like reference charactersdesignate corresponding parts throughout and wherein,

-,Fig. l is a circuit diagram featuring the central station equipmentfor selecting a destination station by apparatus embodying the presentinvention;

Fig. 2 is a fragmentary front elevation of a start-stop signaling"system keyboard apparatus having applied thereto a station selectingdial according to the present invention;

Fig. 3 is a plan view of the apparatus illustrated in Fig. 2;

L Fig. 4 is a side elevation of the apparatus illustrated in Fig. 2; 4

Fig. 5 is a'detailed rear elevation of the rotary dial mechanismaccording to the present invention;

Fig. 6 is a timing diagram illustrating typical signal curves ofstart-stop permutation code signals, and

Fig. '7 is a perspective diagram of certain operating members whichrelate to the present invention shown separate from the telegraphkeyboard.

In the accompanying drawings the reference character II denotesgenerally a rotary dial type of station selecting switch. Essentiallythis unit is comprised of a disc [2 which i integrally associated with astub shaft I3, Fig. 4, and is provided with the ten finger tip receivingapertures, one

representing each numerical integer of the deci .mal series.

Shaft I3 is journaled in 1a bushing 14 which in turn is secured within acentral opening of an en-..

closure case I5, the latter'membenas best viewed in Figs. 3 and 4, beingsupported in an inclined position by means of asuitable supportingbracket [6. Within the case 15, shaft [3 carries integrally associatedwith it a ratchet wheel ll having teeth which correspond in number anddisposition to the finger engagement openings 51 f the finger wheel 12.

' As with conventional telephone dials, the unit I! is provided with afinger stop I8. The latter member is here formed of an armextensionoriginating from lever 19 that is rotatably supported upon said shaftl3. Stop I8 is rotatable through a slight angular distance as determinedby the limiting pins 2i and 22 against theformer of which said stop I8is urged by a spring 23. Integral with lever l9 are two cars indicated24 and 25, Fig. 5, the latter of which pivotally supports a pawl lever26 as at pivot 21 and the former of which provides an anchor point for aspring 28 the other end of which is hooked as at 29 to the uppermostextremity of said pawl lever 26.

Pawl lever 26 is limited in its counterclockwise rotation about pivot 21as urged by the afore-described spring 28 when-its uppermost extremityencounters the stop lug 3| which in turn may also be integrally formedwith the aforedescribed lever l9. Upon the rotation, of lever l9 as whenits finger stop extremity I8 is engaged duringv the final degrees ofmovement of finger wheel [2, pawl lever 26 will be moved bodily upwardwith pivot 21 advancing in a counterclockwisev direction asviewed inFig.5 so that tooth 32 of pawl lever 26, the upper .edge of whichisinclined as indicated in Fig.- 5, encounters the extremity 33 of abell crank lever 35, Fig. 4, there will result .the clockwise rotationof said pawl lever 26 about its pivot 27 and in opposition to the returnspring 28 as it accordingly yields to the extending portion 33 of hellcrank lever 35.

Reiterating, the finger wheel I2 is operated by inserting a finger intoone or the dial openings !v which is opposite a numericaldigit'corresponding to an identifying character of the station sought,and the finger wheel isrotated in a clockwise direction as viewed inFigs. 2 and3,.counter clockwise as viewed in Figs. 5 and 7. Thismovement causes disc l2 and ratchet wheel I! to beIconcurrentlydisplaced to a significant angular position as detent arm'34 ridesove'ra corresponding number of teeth iniatch'e't wheel l1, indicativeof thedigit thus operated. The finger upon encounter -ing stop piece I8 movesthe latter member a distance corresponding to the space between. stoppins 2| and 22 and the finger I is withdrawn. {thereupon lever. l9,being. under tension: of issies iis e rrdeset ea endeavors to return toits original position as illustrated in the drawings and in so doing,pawl 26 is carried downwardly causing its tooth projection 32 to engagethe extremity 33 of bell crank. 35 and to. rock the latter in acounterclockwise direction, Fig. 4, about its pivot 36 which motion ismildly resisted by the lever return-spring 31. Pawl 26 continues toengage extremity 33 thereby holding lever 3335 in its counterclockwiseposition (as viewed in Figs. 4 and 7) until arm 61, integral withratchet I1, re-

: turns to cooperate with projection 68 to disengage pawl 26 fromextremity 33, as will hereinafter appear.

The movement on the part of bell crank 35 is then immediately translatedinto a counterclockwise motion of the character M operating bail 38,Figs. 2, 4, and '7. As bail 38 is rocked in a counterclockwisedirection, Fig. 2, its light acting return spring 39 becomes distendedand its remote extremity 4| engages and depresses key lever 42 wherebythere is generated, through the normal operation or the transmittermechanism, a permutation code signal corresponding to the character M asthis key lever is identified, Fig. 3.

A keyboard apparatu for transmitting signals of the type illustrated-incurve A of Fig. 6 is more fully described and explained in U. S. Patent1,595,472. For the purpose of explaining the application of the instantinvention, it will sui'fice to state that upon the operation of any oneof the key levers such as the particular key lever M indicated by thereference character 42, there is conditioned a set of five code barseach one of which supervises the performance of an associated goose-necklever 43, Fig. 2, while also as a result of the operation of any one ofsaid set of key levers there is affected a leftward movement on the partof common release bar 44, Fig. 4, the rotation of a trip lever 45, andultimately the release of a declutching element 46. In consequence ofthe release motion on the part of lever 46, clutch elements 4'! and 48are brought together so that .set of goose-necks 43 each of which inturn controls an individual pair of contacts of a series which arearranged in a parallel alignment, In addition to this utility, however,cam sleeve 49 in accordance with the instant invention performs afurther purpose as will now be described.

One of the cams of assembly 49 has been especially indicated 5|. Againstthe periphery of this cam there rides a follower roller 52 which, asbest indicated. in Fig. 2, is carried by one arm 53 of abell crankmember whose other arm. 54 is pivotally connected to apawl. 55, theextremity of which is indicated 56 in Fig. 5. f

In consequence of the afore-described arrangement, as cam 5| is rotated,there results a horizontal reciprocation of pawl 55 which, with' itsextremity 56 engages consecutively the teeth of ratchet wheel l1 causingthe latter member to be-rotated in a clockwise direction, as viewed inFigs. 5 and '7 (counterclockwise asviewed in Figs. 2 and 3) one step ata time. each impulse or character M signalis transmitted during therotation of. cam assembly 49, so also by reason of the horizontalactuation of pawl 55 and through its engagement with ratchet wheel l1,there is effected a restoration of the finger wheel 12 one step at a,time until the normal or zero position is resumed.

It will be recalled that finger wheel 12 when rotated in a clockwisedirection as viewed in Figs. 2 and 3 is capable of a total movementcorre sponding to a certain number of composite digit movements eachequal angularly to the distance between successive finger holes 51 ofwhich there are ten in the conventional type of dial illustrated andthat the final degree of movement of any station selecting operationresults, in addi: tion to the rotation of finger wheel l2, in themovement of finger stop 18 through a limited distance as represented bythe two stop pins2'l and- 22. When the operators finger is withdrawn,finger stop [8 being urged by the return spring 23 immediately seeks toresume the position as indicated in Fig. 5 whereat it rests against thestop pin 2|. It is to be noted that during the operation of linger stopmember I8 when it'was rotated counterclockwise (Fig. 5) pawl 32 throughits articulation at pivot 2'1 with an ear 25 which is integral with armI9 is caused to be moved upwardly until its shoulder portion 32overtakes the extremity 33 of bell crank lever 35. In passing over thisextremity spring 28 yields sufficiently to permit said pawl 26 a slightclockwise movement about pivot 21 but after its shoulder 32 comes intothe clear again pat/13126 resumes its relative position to arm H! as{indicated and shoulder 32 is placed above said extremity 33 of bellcrank 35 awaiting the release of finger piece 18. As a result of theinfluence of spring 23, when the operators finger is removed, the entireassembly including arm l9 and pawl 25 are rotated clockwise, Fig. 5, asbefore stated. Shoulder of pawl 32 now positively engages the extremity33 of hell crank lever 35 and causes the latter member to be rockedcounterclockwise about its pivot 36 as viewed in Fig. 4. Presently stoparm l9 encounters the limit pin 2| and {its movement is thereat arresteddetermining thereby the extent of rotation of bell crank 35 whichrotation is opposed by the return spring 3'1. In consequence of thecounterclockwise rotation (Fig. 4) of hell crank member 33-35 itsfarthest extremity which underlies one arm 64 of the bail lever 38causes said arm to be raised against the tendency of a return spring 39,Fig. 2, effecting the depression of its key-lever actuating extremity Mas well as the rotation of its transverse bail portion 59. At the end ofbail portion59 uppermost in Fig. 3 there is integrally formed a trip arm6i which carries the adjustable screw 62 for engaging the horizontallyextending lug 63 as indicated also in Fig. 4. I

In consequence of the operation of lever 38 there are efiected tworesults. Firstly, key lever 42 is depressed, effectively reproducing themain ual actuation for transmitting the alphabetical character M andsecondly the clutch trip dtf'fis rotated which results in the release ofspring actuated driven clutch member 48 so that, it comes intoengagement with clutch driving member 41.

In accordance with the conventional operation of keyboard telegraphtransmitting appater signal. In other words, to eiTect the transmissionof a number of character signals it is necessary to depress any keylever and to permit the same to resume its normal position a number oftimes corresponding to the number of signals to be transmitted. Thissafeguard is usually obtained by the provision of a trip releasemechanism in connection with clutch 47-48.

It is now proposed by providing the extension SI of bail 38 and bywithdrawing clutch trip 46 at the same time that key lever 42 isdepressed to permit cam assembly 49 to rotate a number of revolutionscorresponding to the number of character M signals which aredesired. i

As cam assembly 49-efiects one revolution after another its-cam 5|, Fig.2, encounters follower roller 52 and rotates bell crank 53 clockwise inopposition to its return spring 66, and as these operations proceedsuccessively the downwardly extending arm 54 of said bell crank causesthe pawl 55 to be reciprocated to and fro. With each rightward movementof pawl 55, Fig. 7, leftward as viewed in Figs. 2 and 3, a succeedingtooth of ratchet wheel I! is engaged and then pulled forward therebycausing the finger wheel l2 to be restored by clockwise rotation, Figs.5 and 7.

When the normal or zero position of finger wheel I2 is ultimatelyattained arm 61 which is carried integrally with ratchet wheel I!engages the projection 88 of pawl 26 causing the latter member to berotated clockwise about its pivot 21 and in opposition to its spring 28.This movement withdraws shoulder 32 from the extremity 33 of hell cranklever 33--35 permitting the lat ter member under the influence of itsrestoration spring 31 to resume its normal position as indicated in Fig.4. In consequence bail 38 is free to resume its normal position underthe influence of spring 39 whereupon bail extremity 4| is withdrawn fromke lever 42 and extremity BI is withdrawn from the horizontal plate 63of clutch trip 46.

In this manner there is effectively reproduced, by the use of atelephone station calling finger wheel l2, a system of transmitting anumber of permutation code character M signals corresponding to the callnumber of impulses in a station selecting signal. As the stationselecting signals emanate from the transmitter apparatus,

generally indicated 68 in Fig, 1, they may, before arriving at thecentral ofiice 69, be regenerated at a repeating station such as the oneindicated H, Typical repeating station apparatus is illustrated in U. S.Patent 2,104,273 and since the station selecting impulses are, in fact,a number of similar start-stop permutation code signals issued inseries, they may be repeated over conventional start-stop apparatus suchas illustrated in this disclosure without distortion.

Attention is directedto curves B and C of Fig. 6, where there is shownrespectively the minimum and maximum peak or tolerance characteristicsof a dial signaling equipment such as is conventionally employed intelephony. Test observations have indicated that any dialing signalhaving a spacing characteristic smaller than that indicated in curve Bor one larger than that indicated in curve C is likely to produce falseresponses in station selecting switches of this type. Accordingly, andsince five unit permutation code signals of the type illustrated by thecurve A are reeeivablein standard telegraph .equipment, 'it has beenfound expedient to utilizea particular code combination which inaccordance with convention has been assigned to the alphabeticalcharacter -M which signal is indicated by the curve D to be utilized inthe purpose of reproducing station selecting impulses of the typenecessary in operating telephone switching equipment. The spacingcharacteristic of the code combination for letter M will, as may benoted by comparing curve D with curves B and C, constitute a spacingimpulse greater in length than the minimum curve B and yet one which isless than the maximum impulse curve C. In composing the stationselecting impulse of three code impulses contiguously arranged includingthe start impulse, it may be noted that a total length ofspacingcurrent, somewhat in excess of a median signal length, is therebyobtained. By observing curve D in comparison with curves B and C one maynotice that a two code impulse signal, which corresponds according tocustom with the code combination for the character V, is also usable asa station selectingv switch operating impulse if preferred. I

There will now be described briefly the circuit of Fig. l to illustratethe application of the present invention in the embodiment discussedabove comprising a central station and a limited number of outlyingstations. The reference character 68 designates a transmitting stationwhich may be a unitary apparatus of the type illustrated in U. S. Patent1,632,297 or of the type illustrated in U. S. Patent 2,177,077. Thisoutlying station in addressing the central ofilce I59 may transmit itssignals over a line in which is located a repeater apparatus II whichmay be of the type shown in U. S. Patent 2,105,173 or of the type shownin U. S. Patent 2,104,273. Either of these classes of repeater apparatuspartakes of the characteristic of signal regenerative repeater, that is,signals received from the outlying station 60 are duplicated andretransmitted from a battery local to the regenerating station II and inthis manner distortion efi'ects caused by conditions inherent in theline are eliminated by a well-known practice of reconstructing theoriginal signals under the control of the transmitter 68 so that as theenter upon the succeeding line directed to the central station the truetheoretical signal pattern is again produced.

At the central station the incoming line passes through the winding of aslow-to-release relay I2, thence over local line 14, contactor I3 andits normal make contact point 15, through the winding of relay I6, toground. As aresult of normal marking current on the line, relay 12 willbecome energized and remain in its attracted condition notwithstandingthe signal interruptions due to the succession of line selecting im-'pulses comprised of a series of character M code combination signals,but relay "IE will intermittently release and attract its armature 11causing the latter element to be actuated from itsfront contact point19.toward its back contactpoint I8 andvice versa.

As a result of the energization of slow-to-release relay 12 there willbe drawn up its armatures SI and 82, the former receding from its backcontact point 83 and engaging its front contact point 84, while thelatter will be attracted to its sole front contact. As a result of theclosure of armature82 with its front contact a circuit will beestablished tor operating the station selecting switch mag n et 86,traceable from grounded front contact .poin-t19 of relay-l8 througharmature", conductor. 81, armature .82,

its front contact of relay [2 which is normally energized, conductor 88to'the junction point 89, conductor 9I, winding of magnet 86 to groundedbattery at 92.

As a result of the operation of magnet 86 intermittently under thecontrol of received signals the station selecting switch will be rotatedin a step by step manner advancing the three wiper brushes 93, 94, andso that they successively engage the contact points 96, 91, and 98,respectively, after the manner of station selecting switchoperation-more thoroughly explained in Kempster B. Millers book ofAmerican Tele phone Practice, fourth edition, chapter XXXIV, published1905.

As operating magnet 86 is alternately energized and de-energized inresponse to the fluctuations of armature 11, the station selectingswitch will advance its above recited wiper brushes until they attain'aposition corresponding to the number of station selecting impulsesreceived, whereupon the station selecting switch will momentarily come.to rest with one of the contact points 98' engaged by its wiper 95 for aperiod sufliciently long to cause the operation of slow-to-operatemagnet 99. This is traceable over an obvious circuit from grounded,battery IIlI winding of slow-to-operate relay 99, line I02, wiper 95 anda particular one of its contact points 98, to the, grounded bridgingcircuit I03. As a result of the operation of relay 99 its two armaturesI04 and I05 will be attracted, the former coming into engagement withthe contact point of contactor I3 and establishing a circuit forconnecting the incoming line to the destination station, at the sametime withdrawing contactor 13 from contact point 15 after the well-knownmanner of make before break switch operation.

Contactor I05 engaging contact point I06 completes a circuit formaintaining energized the station selecting operating magnet 86. Thiscircuit is traceable from grounded battery 92, through the winding ofrotary switch operating magnet 86, conductor 9| to the junction point89, thenceover conductor 88,. front contact of armature-82, conductor8'1, armature 11, (which is now released) contact point 18, contactpoint I06 and its aramature I 05 (which is now at: tracted) conductorI08, contact point 84 to grounded armature 8| (which is still attractedbecause normally current is flowing in the line). When contactor I3 iswithdrawn from contact point I5 as above described there results thedeenergization of relay I6. As a result of the attraction of armatureI04 with the contact point of contactor l3 incoming line through thewinding of relay 12 and local conductor 14 is continued over the contactpoint of contactor 13 and its associated armature I04, conductor I09,wiper 98 and one of its contact points corresponding to the selectedstation, thence out over one of the line conductors III- to a particulardestination station II2;, IIZA, etc.

, After the communicationwith the destination station II2, II2A,'etc.,has been-com-pleted,-the line conductor may be broken at-any pointeitherbetween the central-station and one of the destination stations orbetween the calling station 68 and the central station, and theapparatus will become restored to zero or normal condition in thefollowing manner. Slow-to-release relayTlZ, being in;ci1-cu it at alltimes,.when,the current is interrupted fora sufiicient'len'gth oiftir'neto dee nergize -s'aid relay' its arm'atures 81 and82.wil l bepermittedto fall back removing ground at ar ground will be introduced again tothe circuit including winding of magnet 86 as follows: from groundedbattery 92, through the winding of magnet 86, conductor 9|, armature H3and contact point H4, conductor I 15 to the bridging circuit of theseveral contact points 91 and wiper 94, thence conductor H6 contactpoint 83 to grounded armature 8|. As a result magnet 86 will becomeenergized again attracting its armature H3 away from contact point H4whereupon the circuit will again be broken for said magnet 86 which willagain release its armature I I3, etc., the operation continuingintermittently until wiper 94 resumes the normal position at which itengages the zero contact point H'I-which does not connect with conductorH5. Since magnet 85 operates all of the wipers 93 to 95, inclusive,there will in this manner be efiected the restoration of the switch tonormal or Zero condition in readiness for a succeeding station selectionoperation.

In illustrating the application of the present invention there has beenchosen for arbitrary illustration the rotary line finder apparatusidentified as Strowger step-by-step switches. To those acquainted withexchange office apparatus it will be evident that other forms of linefinder systems, such as the panel or cross-bar selectors,

are equally adaptable for use and that multiple digit selection may beobtained by the application of known circuit arrangements.

While the present invention has been explained and described withreference to but a single embodiment, it is to be understoodnevertheless that numerous variations and modifications may beincorporated without substantial departure from the present invention.Accordingly, it is not intended to be limited to the specific details ofthe foregoing specification nor to the particulars of the accompanyingdrawings except as indicated in the hereunto appended claims.

What is claimed is: 1. In a telegraph station selection system, a

central office comprising a selector switch, intermittent-signal.controlled means for actuating said selector switch, a plurality ofoutlying stations, a telegraph keyboard transmitter at each outlyingstation, and a dial apparatus also at each outlying station forautomatically actuating said keyboard transmitter for producingstep-bystep digital signals to actuate said selector switch to select,for communication with a calling outlying station, any other of saidplurality of outlying stations.

2. In .a telegraph station selection system, a central oflicecomprisinga selector switch, stepby-step mechanism for operating saidselector switch, a plurality of outlying stations, a telegraph keyboardtransmitter at said outlying stations for producing intelligencesignals, and a dial, apparatus also at each outlying station forautomatically actuating said keyboard transmitter to generate asuccession of intelligence signal impulses under a single manipulationof said dial apparatus to actuate said step-by-ste mechanism of saidselector switch for stablishing communication with one of said outlyingstations.

3. In a telegraph system, a central station, a

mature 8| from the circuit which had been holdplurality of outlyingstations, telegraph apparatus at each of said outlying stations forsending and receiving start-stop equal length permutation code signals,switching means at said central station for establishing communicationautomatically between two of said plurality of outlying stations underthe control of step-by-step signals, and dial apparatus at each of saidoutlying stations responsive to a single manipulative action forautomatically actuating said telegraph apparatus forgenerating aplurality of groups of said equal length code signals to operate saidswitching means step-by-step.

4. In a telegraph communication system, a central station, a pluralityof outlying stations, telegraph apparatus at each of said outlyingstations for sending and/or receiving start-stop equal lengthpermutation code signals, switching means at said central stationcontrollable by any calling one of said plurality of outlying stationsfor establishing communication automatically with another one of saidplurality of outlying stations under operation by. step-by-step signals,

and dial apparatus at each of said outlying stations responsive to asingle manipulative operation for automatically actuating said telegraphapparatus for generating predeterminedly said equal length permutationcode signals to operate step by step said switching means.

, 5. In a telegraph system, a central ofiice, a plurality of subscriberstations, line conductors connecting said stations with said office,communication apparatus including a set of telegraph key levers at eachsaid subscriber stations, means associated with each of saidcommunication apparatuses including. a dialing device for selectivelyactuating one of said telegraph key levers automatically fortransmitting from said subscribers station over its line conductor aseries of equal length permutation code impulses to said centralstation, and means at said central'station responsive to said series ofequal length permutation code impulses for establishing a connectionwith another'line conductor extending therefrom. I

6. In an intercommunication system, an exchange station, a pluralityofsubscriber stations, line conductors connecting said subscribersstations with said exchange station, selector switch equipment at saidexchange station, a telegraph I keyboard transmitter at each of saidsubscriber stations, and a dial apparatus also at each of saidsubscriber stations for automatically actuating said keyboardtransmitter to generate impulses to operate said selector switchequipment at said exchange station and establish a connection withanother line conductor extending therefrom.

7. In a telegraph system, a plurality of printing telegraph stations,telegraph signal transmitters at each of said stations, a centralofiice, line conductors extending from said central office to saidtelegraph stations, selecting apparatus at said central ofi'ice forautomatically selecting the line conductor of one of said plurality ofstations for communication, and means for controlling said-selectingapparatus including a calling dial at each of said plurality ofstations, and equipment interconnected with said dial for actuating saidtelegraph signal transmitter to generate a number of signals inaccordance with the degree of rotation of said dial.

LOUIS M. POTTS.

